Inspection methods for inspecting transparent bodies include a plate glass defect inspection method disclosed in Patent Document 1. In the plate glass defect inspection method disclosed in Patent Document 1, plate glass is illuminated from its lateral end face, and an image of a plate glass surface is captured by an image capturing optical system from the surface side of the plate glass to detect brightness of the image per given area, thus determining a defect. This inspection method utilizes a phenomenon in which when an internal defect such as a bubble or a foreign substance exists in the plate glass, light is irregularly reflected by the defect and emitted outside from upper and lower surfaces of the plate glass.
Patent Document 1 further discloses a method in which an illumination light source is placed adjacent to one side of plate glass, an image capturing optical system is placed adjacent to the other side of the plate glass, an image of the plate glass is captured by the image capturing optical system, and the image formed based on transmitted light is processed, thus detecting a defect.
Moreover, Patent Document 2 discloses a transparent body detection system for detecting a transparent foreign substance inside a transparent bottle (which is an empty bottle or a bottle containing transparent liquid). The transparent body detection system disclosed in Patent Document 2 includes: an illumination device for applying planar light to the bottle that is vertically put; and a light projection side polarizing plate, provided over a light projection surface of the illumination device, for polarizing the planar light in a particular direction. The system further includes a light receiving polarizing plate and a television camera, which are located opposite to the light projection side polarizing plate with the bottle located at the center. The light projection side polarizing plate and the light receiving polarizing plate are set so that polarization directions thereof coincide with each other. The transparent body detection system disclosed in Patent Document 2 rotates the bottle, captures images thereof repeatedly by the television camera during one rotation of the bottle, and determines existence of a transparent foreign substance when the image captured by the television camera has a region where a dark chunk is seen. Furthermore, Patent Document 2 also discloses a case in which the light projection side polarizing plate and the light receiving polarizing plate are set so as to be orthogonal to each other, and existence of a transparent foreign substance is determined when an image has a region where a bright chunk is seen. Besides, Patent Document 2 discloses a slide actuator for sliding the polarizing plate within a horizontal plane, and a slide actuator controller for driving and controlling the slide actuator.